34-1: Flow of Charge -When the ends of an electric conductor are at different electric potentials, charge flows from one end to the other. -Potential difference – difference in potential (voltage) -The flow of charge will continue until both ends reach a common potential. -With no potential difference, there is no longer a flow of charge through the conductor. -To attain a sustained flow of charge in a conductor, potential difference must be maintained while charge flows from one end to the other. - 34-2: Electric Current -Electric current – the flow of electric charge. -Electrons carry the charge through the circuit of the solid conductors because they are free to move through the atomic network. -Protons are bound inside atomic nuclei that are more or less locked in fixed positions. -In fluids, positive and negative ions and electrons compose the flow of electric charge. -Ampere – the measure of electric current; SI unit: A. An ampere is the flow of 1 coulomb of charge per second. -Current-carrying wire does not have a net electric charge.
34-3: Voltage Sources -Charges do not flow unless there is a potential difference. -Voltage source – something that provides a potential difference
The voltage, V, creates current I using resistance, R.http://upload.wikimedia.org/wikipedia/commons/thumb/a/a0/Ohms_law_voltage_source.svg/150px-Ohms_law_voltage_source.svg.png
-- It is not practical to have a voltage source whose two potentials equalize in one brief surge of moving charges. -Dry cells, wet cells, and generators are capable of maintaining a steady flow.They supply energy that allows charges to move. -In dry cells and wet cells, generators supply energy that allows charges to move. -Generators convert mechanical energy to electric energy. -Voltage provides electric pressure to move electrons between the terminals in a circuit. -Power lines use electric converters to provide 120 volts delivered to home outlets.The alternating potential difference between the two holes in the outlet has an average of 120 volts. -Charges flow through a circuit because of an applied voltage. -Voltage does not move; only charges
34-4: Electric Resistance -The amount of current flowing in a circuit depends on the voltage provided by the voltage source.Also dependant on electric resistance. -Electric resistance – the resistance that the conductor offers to the flow of charge.
Resistance lowers the flow of current. http://mirror.unej.ac.id/onnowpurbo/orari-diklat/teknik/handbook/radio-amateur-handbook-1922_files/fig031.png
-The resistance of a wire depends on the conductivity of the material used in the wire as well as the thickness and length of the wire. -Thick wires have less resistance than thin wires. -Longer wires have more resistance than short wires. -The greater the motion of atoms within the conductor, the greater resistance the conductor offers to the flow of charge. -For most conductors, increased temperature means increased resistance.
34-5: Ohm’s Law -The current in a circuit is directly proportional to the voltage impressed across the circuit, and it is inversely proportional to the resistance of the circuit. oCurrent = (voltage)/(resistance) -Ohm’s Law – the relationship between voltage, current, and resistance. o1 ampere = 1 (volt/ohm)
34-6: Ohm’s Law and Electric Shock -Shock in the human body is caused by current passing through the body. -The resistance of the human body is dependent on its condition and ranges from about 100 ohms (soaked in salt water) to 500,00 (totally dry).
Current in amperes
Effect
.001
Can be felt
.005
Painful
.010
Involuntary muscle spasms
.015
Loss of muscle control
.070
Serious heart disruption, most likely fatal if lasting for more than 1 second
-For birds sitting on an electrical wire to feel a shock, there must be a difference in electric potential.They must be touched two wires.
Birds will electrocute themselves if they land on two wires with differing electric potential. http://www.birdwatchersgeneralstore.com/ElectricLines.htm
34-7:Direct Current and Alternating Current -Direct current – a flow of charge that always flows in one direction.Example: battery (the terminals of the battery always have the same sign of charge)
-Voltage in ac in North America is normally 120 volts -Voltage in ac in Europe is 220 as the standard -Most electric service in the US operates on a three-wire system; one wire at 120 volts positive, one wire at 0 volts (neutral), one wire at negative 120 volts.
34-8: Converting AC to DC -Diode – tiny electronic device used as a one-way valve to allow electron flow in only one direction -A capacitor slows changes in current flow.
34-9: The Speed of Electrons in a Circuit -An electric field is established inside the wire when a batter or generator is connected to a metal wire -The electric field outside the wire is determined by the location of electric charges. -The electric field inside the wire runs directly along the wire -In dc circuit, the electric field lines are maintained in one direction in the conductor -In ac circuit, the conduction electrons don’t make any net progress in any direction.
34-10: The Source of Electrons in a Circuit -The source of electrons in a circuit is the conduction circuit material itself. -Energy (not electrons) carries from ac outlet into what is plugged in -Energy is carried by the electric field and causes a vibration of the electrons that already exist in the plugged in object -When shocked by an electric shock, energy causes free electrons in your body to vibrate in unison.
34-11: Electric Power -Electric power – the rate at which electric energy is converted into another form oElectric power = current * voltage -Power is expressed in watts when voltage is in volts and current is in amperes o1 watt = (1 ampere) * (1 volt)
Physics, Period 8
Chapter 34: Electric Current
Vocabulary
34-1: Flow of Charge
- When the ends of an electric conductor are at different electric potentials, charge flows from one end to the other.
- Potential difference – difference in potential (voltage)
- The flow of charge will continue until both ends reach a common potential.
- With no potential difference, there is no longer a flow of charge through the conductor.
- To attain a sustained flow of charge in a conductor, potential difference must be maintained while charge flows from one end to the other.
-
34-2: Electric Current
- Electric current – the flow of electric charge.
- Electrons carry the charge through the circuit of the solid conductors because they are free to move through the atomic network.
- Protons are bound inside atomic nuclei that are more or less locked in fixed positions.
- In fluids, positive and negative ions and electrons compose the flow of electric charge.
- Ampere – the measure of electric current; SI unit: A. An ampere is the flow of 1 coulomb of charge per second.
- Current-carrying wire does not have a net electric charge.
34-3: Voltage Sources
- Charges do not flow unless there is a potential difference.
- Voltage source – something that provides a potential difference
-- It is not practical to have a voltage source whose two potentials equalize in one brief surge of moving charges.
- Dry cells, wet cells, and generators are capable of maintaining a steady flow. They supply energy that allows charges to move.
- In dry cells and wet cells, generators supply energy that allows charges to move.
- Generators convert mechanical energy to electric energy.
- Voltage provides electric pressure to move electrons between the terminals in a circuit.
- Power lines use electric converters to provide 120 volts delivered to home outlets. The alternating potential difference between the two holes in the outlet has an average of 120 volts.
- Charges flow through a circuit because of an applied voltage.
- Voltage does not move; only charges
34-4: Electric Resistance
- The amount of current flowing in a circuit depends on the voltage provided by the voltage source. Also dependant on electric resistance.
- Electric resistance – the resistance that the conductor offers to the flow of charge.
- The resistance of a wire depends on the conductivity of the material used in the wire as well as the thickness and length of the wire.
- Thick wires have less resistance than thin wires.
- Longer wires have more resistance than short wires.
- The greater the motion of atoms within the conductor, the greater resistance the conductor offers to the flow of charge.
- For most conductors, increased temperature means increased resistance.
34-5: Ohm’s Law
- The current in a circuit is directly proportional to the voltage impressed across the circuit, and it is inversely proportional to the resistance of the circuit.
o Current = (voltage)/(resistance)
- Ohm’s Law – the relationship between voltage, current, and resistance.
o 1 ampere = 1 (volt/ohm)
34-6: Ohm’s Law and Electric Shock
- Shock in the human body is caused by current passing through the body.
- The resistance of the human body is dependent on its condition and ranges from about 100 ohms (soaked in salt water) to 500,00 (totally dry).
34-7: Direct Current and Alternating Current
- Direct current – a flow of charge that always flows in one direction. Example: battery (the terminals of the battery always have the same sign of charge)
- Alternating current – electrons move first in one direction and then in the opposite direction. Example: commercial ac circuits
- Voltage in ac in North America is normally 120 volts
- Voltage in ac in Europe is 220 as the standard
- Most electric service in the US operates on a three-wire system; one wire at 120 volts positive, one wire at 0 volts (neutral), one wire at negative 120 volts.
34-8: Converting AC to DC
- Diode – tiny electronic device used as a one-way valve to allow electron flow in only one direction
- A capacitor slows changes in current flow.
34-9: The Speed of Electrons in a Circuit
- An electric field is established inside the wire when a batter or generator is connected to a metal wire
- The electric field outside the wire is determined by the location of electric charges.
- The electric field inside the wire runs directly along the wire
- In dc circuit, the electric field lines are maintained in one direction in the conductor
- In ac circuit, the conduction electrons don’t make any net progress in any direction.
34-10: The Source of Electrons in a Circuit
- The source of electrons in a circuit is the conduction circuit material itself.
- Energy (not electrons) carries from ac outlet into what is plugged in
- Energy is carried by the electric field and causes a vibration of the electrons that already exist in the plugged in object
- When shocked by an electric shock, energy causes free electrons in your body to vibrate in unison.
34-11: Electric Power
- Electric power – the rate at which electric energy is converted into another form
o Electric power = current * voltage
- Power is expressed in watts when voltage is in volts and current is in amperes
o 1 watt = (1 ampere) * (1 volt)